Method and apparatus for restart communication between network elements

ABSTRACT

A method and apparatus for the restart communication between network elements are described. In one embodiment, a method for restarting communication between a first network element and a second network element in a network comprises transmitting a modified hello packet to the second network element. The modified hello packet includes a time value that is greater than a time value of a hello packet that was transmitted to the second network element prior to International-System-International-System (IS-IS) network communications in the first network element becoming non-operational. The method also including updating routing information within the first network element through transmission of Complete Sequence Number Packets of the IS-IS standard to the second network element, independent of tearing down a communication link between the first network element and the second network element after IS-IS network communications in the first network element have become non-operational.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This is a Continuation of prior application Ser. No. 09/873,037,filed Jun. 2, 2001.

FIELD OF THE INVENTION

[0002] The invention relates to the field of communications. Morespecifically, the invention relates to a method and apparatus forrestart communication between network elements.

BACKGROUND OF THE INVENTION

[0003] Communication networks are generally comprised of two or moreindividual network elements, such as a router or switch, coupledtogether. Network elements generally contain a number of line cards andcontrol cards that are used to transmit data through the networkelement. The line cards and control cards generally contain a number ofcircuits to control the transmission of such data.

[0004] International-System-International-System (“IS-IS”) is a linkstate interior gateway protocol originally developed for routingISO/CLNP (“International Organization for Standardization/ConnectionlessNetwork Protocol”) packets among network elements. IS-IS is used tocontrol routing in some networks, and can use a ‘shortest path first’algorithm for determining a particular data route within the network. Inparticular, network elements typically employ the IS-IS standard tocommunicate their routing information among one another. Several typesof network configurations are supported by IS-IS, e.g., broadcast(network elements are coupled to a single connection medium, such as anEthernet connection), and point-to-point (network elements are connectedto one another directly).

[0005] The IS-IS standard utilizes several different types of datapackets for the transmission of routing information. For example, hellopackets (“IIHs”) are used to establish and maintain neighbor adjacencybetween two network elements. Complete sequence number packets (“CSNPs”)contain sequence numbers of all routing information of a network so thatan individual network element can determine whether it needs to updateits own internal ‘picture’ of the network. Partial sequence numberpackets (“PSNPs”) contain the sequence numbers for the routinginformation for one particular network element. Link state packets(“LSPs”) contain the actual routing information for a particular networkelement, i.e., to what other network element(s) or network(s) that it isconnected.

[0006] Also, ‘hello’ packets or ‘heartbeat’ messages are typically sentat regular intervals by network elements to other network elements totell the recipient network elements that the sending network element isstill operational. The recipient network element then expects to receiveanother ‘hello’ packet from the sender within the same period of time(which is adjustable). If these ‘hello’ packets are not received withinthe time period set, the recipient assumes that the transmitting networkelement is non-operational for purposes of routing data and accordingly,tears down the communication link between itself and the transmittingnetwork element. Once the transmitting and recipient network element areagain able to communicate the communication link between the two must bereconstructed. Moreover, once the communication link is reestablished,the two network elements typically exchange routing information in orderto ensure that such information is up-to-date. Disadvantageously, thisprocess of tearing down a communication link, establishing a newcommunication link and exchanging routing information between the twonetwork elements can be time consuming, thereby potentially causing theloss of data packets within the network that could be transmittedbetween the two network elements.

SUMMARY OF THE INVENTION

[0007] A method and apparatus for the restart communication betweennetwork elements are described. In one embodiment, a method forrestarting communication between a first network element and a secondnetwork element in a network comprises transmitting a modified hellopacket to the second network element. The modified hello packet includesa time value that is greater than a time value of a hello packet thatwas transmitted to the second network element prior toInternational-System-International-System (IS-IS) network communicationsin the first network element becoming non-operational. The method alsoincluding updating routing information within the first network elementthrough transmission of Complete Sequence Number Packets of the IS-ISstandard to the second network element, independent of tearing down acommunication link between the first network element and the secondnetwork element after IS-IS network communications in the first networkelement have become non-operational.

[0008] In an embodiment, a network element includes a memory.Additionally, the network element includes a heartbeat unit coupled tothe memory. The heartbeat unit is to transmit a modified heartbeatpacket to a different network element in a network. The modifiedheartbeat packet is to be stored in the memory and is to include a timevalue that is greater than a time value of a heartbeat packet that is tobe transmitted to the different network element prior toInternational-System-International-System (IS-IS) network communicationsin the network element becoming non-operational. The network elementalso includes a reinitialize unit coupled to the heartbeat unit. Thereinitialize unit is to update routing information within the networkelement through transmission of Complete Sequence Number Packets of theInternational-System-International-System (IS-IS) standard to thedifferent network element, independent of tearing down a communicationlink between the network element and the different network element afterIS-IS network communications the network element have becomenon-operational.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Embodiments of the invention may be best understood by referringto the following description and accompanying drawings that illustratesuch embodiments. The numbering scheme for the Figures included hereinare such that the leading number for a given element in a Figure isassociated with the number of the Figure. For example, network 100 canbe located in FIG. 1. However, element numbers are the same for thoseelements that are the same across different Figures.

[0010] In the drawings:

[0011]FIG. 1 is a block diagram illustrating an embodiment of abroadcast network configuration that incorporates embodiments of thepresent invention.

[0012]FIG. 2 illustrates portions of network elements 102-112, accordingto embodiments of the present invention.

[0013]FIG. 3 is a block diagram illustrating portions of control card220, according to embodiments of the present invention.

[0014]FIG. 4 illustrates a flow diagram for maintaining communicationbetween network elements, according to embodiments of the presentinvention.

[0015]FIG. 5 illustrates a flow diagram for restart communication of anetwork element (that is the designated network element) in a broadcastnetwork configuration using the IS-IS standard after the IS-IScommunications of network element has been non-operational, according toembodiments of the present invention.

[0016]FIG. 6 illustrates a flow diagram for restart communication of anetwork element (that is not the designated network element) in abroadcast network configuration using the IS-IS standard after the IS-IScommunications of the network element has been non-operational,according to embodiments of the present invention.

[0017]FIG. 7 is a block diagram illustrating an embodiment of apoint-to-point network configuration that incorporates embodiments ofthe present invention.

[0018]FIG. 8 illustrates a flow diagram for restart communication of anetwork element in a point-to-point network configuration using theIS-IS standard after the IS-IS communications of the network element hasbeen non-operational, according to embodiments of the present invention.

[0019]FIG. 9 illustrates a flow diagram for updating routing informationwithin a network element, according to embodiments of the presentinvention.

DETAILED DESCRIPTION

[0020] A method and apparatus for the restart communication betweennetwork elements are described. In the following description, forpurposes of explanation, numerous specific details are set forth inorder to provide a thorough understanding of the present invention. Itwill be evident, however, to one skilled in the art that the presentinvention may be practiced without these specific details.

System Description

[0021]FIG. 1 is a block diagram illustrating an embodiment of abroadcast network configuration that incorporates embodiments of thepresent invention. In particular, FIG. 1 illustrates network 100 thatincludes broadcast network transmission line 114, network element 102,network element 106, network element 108, and network element 112 suchthat network elements 102, 106, 108, and 112 are coupled together viaconnection to broadcast network transmission line 114, according toembodiments of the present invention. Network element 104 and networkelement 110 are coupled to network elements 102 and 108, respectively.In an embodiment, network elements 102-112 can be routers, switches,bridges, or other types of network elements that switch data across anetwork. In another embodiment, network 100 is a system in which networkelements 102-112 share routing information using the IS-IS standard. Ina further embodiment, network elements 102-112 are coupled to othernetwork elements that may or may not be coupled to broadcast networktransmission line 114.

[0022] In an embodiment, broadcast network transmission line 114 employsthe Ethernet standard. However, embodiments of the present invention arenot so limited. Examples of other types of broadcast media includes, butis not limited to, Fiber Distributed Data Interface (FDDI) and TokenRing. In one embodiment, network 100 transmits data traffic among thedifferent network elements employing the Synchronous Optical Network(“SONET”) standard or Synchronous Digital Hierarchy (“SDH”). However,embodiments of the present invention are not so limited, as data trafficamong the different network elements can be transferred using othertypes of transmission standards. Examples of other types of transmissionstandards can include, but are not limited to, T1, T3, Data Signal(“DS”)3, and DS1 signals.

[0023] The architecture and configuration of network 100 is by way ofexample and not by way of limitation, as embodiments of the presentinvention can be incorporated in other types of systems. For example,other such systems could incorporate less or more network elements intothe network and/or network elements attached thereto. Further, adifferent configuration of the network elements could exist. Moreover,embodiments of the system in which the present invention is implementedare not limited to the network architecture as illustrated in FIG. 1.Examples of other types of network architectures that can incorporateembodiments of the system in which the present invention is implementedinclude, but are not limited to, a point-to-point configuration (seediscussion of FIG. 5 below), point-to-multipoint configuration, and ahub configuration.

Network Element Description

[0024]FIG. 2 illustrates portions of network elements 102-112, accordingto embodiments of the present invention. As shown, network elements102-112 (hereinafter, “network element 102”) include line cards 202,204, 206, and 208, control card 220, and packet mesh 210. For example,line card 202 is coupled to line card 204 through packet mesh 210. Inone embodiment, packet mesh 210 is a switch fabric, which includes afull mesh such that each of line cards 202-208 is coupled to oneanother. However, embodiments of the present invention are not limitedto a full mesh for the transmission of data among line cards 202-208, asany type of switching method that switches based on an addressing schemecan be incorporated into embodiments of the present invention. Thenumber of contents and connections of network element 102 illustratedare for the purpose of simplicity and not by way of limitation, as agreater or lesser number of contents or connections may be presentwithin network element 102.

[0025] Control card 220 is coupled to exchange data with each of linecards 202-208. Each of line cards 202-208 is coupled to receive andtransmit data. In one embodiment, line cards 202-208 may be connected toan optical line transmitting SONET OC-N signals. Moreover, in anembodiment, line cards 202-208 may be connected to an electrical linesuch as a T1, T3, E1, E3, Ethernet, Gigabit Ethernet, etc. However,embodiments of the present invention are not limited to theabove-described examples, as any other type of optical or electricaldata transmission can be incorporated into embodiments of the presentinvention.

[0026]FIG. 3 is a block diagram illustrating portions of control card220, according to embodiments of the present invention. In particular,FIG. 3 illustrates control card 220, which includes routing processor302, configuration processor 304, memory 306, reinitialize unit 308,heartbeat unit 310 and routing information base unit 312, which arecoupled together, In one embodiment, memory 306 is random access memory(“RAM”). Additionally, in an embodiment, reinitialize unit 308,heartbeat unit 310 and routing information base unit 312 can beprocesses that can reside within memory 306 and/or routing processor 302and can be executed within routing processor 302 and configurationprocessor 304. However, embodiments of the present invention are not solimited, as reinitialize unit 308, heartbeat unit 310 and routinginformation base unit 312 can be different types of hardware (such asdigital logic) executing the processing described therein. Theconfiguration illustrated by FIG. 3 is by way of example and not by wayof limitation. For example, in another embodiment, routing processor 302and configuration processor 304 each have their own memory.

Operation of Network Elements 102-112 in a Broadcast NetworkConfiguration

[0027]FIG. 4 illustrates a flow diagram for maintaining communicationbetween network elements, according to embodiments of the presentinvention. Returning to FIG. 1 to help illustrate, the flow diagram ofFIG. 4 will be described in terms of maintaining communications betweennetwork element 102 (acting as the transmitting network element) andnetwork element 112 (acting as the receiving network element). Method400 commences with the creation of a ‘hello’ packet by heartbeat unit310 of network element 102, at process block 402.

[0028] These ‘hello’ packets act as heartbeat messages between twonetwork elements. In particular, these packets can be sent at regularintervals by network elements to other network elements to tell thereceiving network elements that the transmitting network element isstill operational. In an embodiment, these ‘hello’ packets include atime value indicating the period of time when the receiving networkelement is to receive another ‘hello’ packet. In one such embodiment,this time value is adjustable by both or either the transmitting orreceiving network element. If this next ‘hello’ packet is not receivedwithin the time period specified within this time value, the receivingnetwork element tears down the communication link between itself and thetransmitting network element, as the receiving network element assumesthat the transmitting network element is no longer operational andtherefore unable to process and route packets.

[0029] Heartbeat unit 310 of network element 102 generates a copy of the‘hello’ packet, at process block 404. Additionally, heartbeat unit 310of network element 102 transmits the ‘hello’ packet to network element112, at process block 406. In one embodiment, this ‘hello’ packetincludes a time value that has been previously configured by eithernetwork element 102 or network element 112 (known as “the default timevalue”). At process block 408, heartbeat unit 310 of network element 102increases the time period stored in the default time value of the copyof the ‘hello’ packet. Moreover, heartbeat unit 310 of network element102 stores the copy of the ‘hello’ packet with the modified time periodwithin memory 306, at process block 410. Network element 102 willgenerally receive a response ‘hello’ packet back from network element112, at process block 412 (assuming that the communication link betweennetwork elements 102 and 112 is still established and network elements102 and 112 are still operational). Network element 102 continues thisheartbeat messaging with network element 112 by transmitting another‘hello’ packet, at process block 402.

[0030] Method 400 was described such that process blocks 404, 408 and410 (the generation, modification and storage of a ‘hello’ packet) areexecuted each time a ‘hello’ packet is generated. However, this is byway of example and not by way of limitation. In other embodiments, thisprocess blocks are executed every Nth time that a ‘hello’ packet isgenerated. For example, in one embodiment, these process blocks areexecuted every 10^(th) time that a ‘hello’ packet is generated.

[0031] However, if the IS-IS communications of one of network elements102 or 112 were to become non-operational, this messaging of ‘hello’packets between the two would cease. FIG. 5 illustrates a flow diagramfor restart communication of a network element (that is the designatednetwork element) in a broadcast network configuration using the IS-ISstandard after the IS-IS communications of network element has beennon-operational, according to embodiments of the present invention. Inparticular, method 500 illustrates a flow diagram of a network elementthat was non-operational with regard to the IS-IS communications and isreinitializing and reestablishing communication with other networkelements in the network. A designated network element is that networkelement within the network that acts in a management capacity for thenetwork and the network elements coupled thereto. Examples of the typeof operations of the designated network element includes, but are notlimited to, distributing and storing routing information among and forthe network elements in the network.

[0032] Method 500 commences with the reading of the modified ‘hello’packets from memory 306 (as illustrated in FIG. 4 above) by reinitializeunit 308 of network element 102, at process block 502. Additionally,reinitialize unit 308 of network element 102 also transmits these‘hello’ packets to those network elements with which network element 102has communication links between, at process block 504. Method 500 willbe described in terms of network element 102 restarting communicationwith one network element (network element 112). This is by way ofexample and not by way of limitation, as the method described isapplicable for a network element attempting to restart communicationwith a number of network elements.

[0033] This transmission of the stored ‘hello’ packets, which have anincreased time period, to other network elements with which there is acommunication link allows the restarting network element more time toreinitialize. In particular, if the restarting network element is ableto transmit a modified ‘hello’ packet to the receiving network elementbefore the default time period (which was transmitted with theunmodified ‘hello’ packets) expires, the restarting network element isable to preclude the receiving network element from tearing down thecommunication link between itself and the restarting network element.Accordingly as will be described in more detail below, this delay intime allows the restarting network element to reinitialize and updatesits routing information without tearing down and reconstructing thecommunication link as well as precluding the exchange of routing databetween the two network elements after reconstruction of thecommunication link in order to restart communications between therestarting network elements and those network elements that it isconnected. In particular, this delay in time allows the restartingnetwork element to reinitialize, which includes waiting for allneighboring network elements to transmit ‘hello’ packets to itself andincludes periodically sending out CSNP packets to update routinginformation therein.

[0034] Moreover, reinitialize unit 308 of network element 102 transmitsa request for routing data to other network elements in the network, atprocess block 506. In an embodiment, reinitialize unit 308 of networkelement 102 transmits this request for routing data using the IS-ISstandard. In one such embodiment, reinitialize unit 308 of networkelement 102 transmits a request for Link State Packets (LSPs) using CSNPpackets under the IS-IS standard. In particular, LSPs can contain actualrouting information for a given network element, such as what othernetwork element(s) and/or network(s) that it is connected.

[0035] Accordingly, reinitialize unit 308 of network element 102receives routing data from the network element(s) in the network, atprocess block 508. In the embodiment wherein a request for LSPs isrequested, reinitialize unit 308 of network element 102 receives anumber of LSPs under the IS-IS standard from the other networkelement(s) in the network. Upon receipt of this routing data from eachof the network elements, reinitialize unit 308 of network element 102updates its routing data with data received from the requesting networkelements, at process block 510. In one embodiment, when the IS-IScommunications of network element 102 became non-operational, itsrouting data was lost. Accordingly, reinitialize unit 308 of networkelement 102 begins recreating its routing data based on that receivedfrom other network elements. In an embodiment wherein the IS-IS standardis employed, network element 102 compares the routing data received fromthe different network elements and maintains the most up-to-date routingdata based on sequence numbers for this routing data.

[0036] Upon receiving routing data from a network element, networkelement 102 determines whether a preset timer has expired, at processdecision block 512. In an embodiment, this preset timer is activatedwhen network element 102 is reinitialized. In one embodiment, the timefor the preset timer is smaller than the time that was modified in themodified ‘hello’ packets. Upon determining that this preset timer hasnot expired, network element 102 returns to process block 506 andtransmits another request for routing data to the other networkelements. In contrast, upon determining that the preset timer hasexpired, network element 102 transmits a first unmodified ‘hello’ packetand resumes normal operation, at process block 514.

[0037] As illustrated, this preset timer within network element 102allows the other network elements time to respond with the requiredrouting data prior to resuming operation. Accordingly, upon resumingoperation when IS-IS based messaging resumes among network element 102and the other network elements in the network, the other networkelements do not know that the IS-IS communications of network element102 has been non-operational. The other network elements, therefore,will not destroy and recreate the communication link between themselvesand network element 102. Moreover, there is no requirement that theother network elements exchange their routing data with network element102 after the reconstruction of the communication link. Accordingly, thedata packets that can be transmitted across the communication linksbetween network element 102 and the other network elements will not haveto be re-routed or lost during the time when the communication link isdestroyed and reconstructed and when the routing data is exchangedbetween the other network elements and network element 102.

[0038]FIG. 6 illustrates a flow diagram for restart communication of anetwork element (that is not the designated network element) in abroadcast network configuration using the IS-IS standard after the IS-IScommunications of the network element have been non-operational,according to embodiments of the present invention. In particular, method600 illustrates a flow diagram of a network element whose IS-IScommunications were non-operational and is reinitializing andreestablishing communication with other network elements in the network.

[0039] Method 600 commences with the reading of the modified ‘hello’packets from memory 306 (as illustrated in FIG. 4 above) by reinitializeunit 308 within network element 102, at process block 602. Additionally,reinitialize unit 308 also transmits these ‘hello’ packets to thosenetwork elements with which network element 102 has communication linksbetween, at process block 604 (as described above in conjunction withFIG. 5). Reinitialize unit 308 also receives Complete Sequence NumberPackets (CSNPs) under the IS-IS standard from the designated networkelement and receives ‘hello’ packets from other network elements in thenetwork, at process block 606. CSNPs include sequence numbers related tothe routing information of the network such that given sequence numberscorrespond to portions of the network, such as the connectivity of agiven network element to other network elements in the network. Inparticular, in one embodiment, the designated network elementperiodically transmits these CSNPs to the other network elements.Accordingly, network element 102 can wait and receive the CSNPs.

[0040] Based on the received CSNPs, reinitialize unit 308 determineswhether it has the most recent version of the LSPs, at process decisionblock 608. In particular, a given sequence number within the CSNPsand/or stored within network element 102 is associated within givenrouting data. For example, a given sequence number could be associatedwith the routing and connectivity of network element 110.

[0041] Upon determining that network element 102 has the most recentversion of the LSPs, reinitialize unit 308 determines whether the presettimer within network element 102 has expired (which is described abovein conjunction with process decision block 512 of FIG. 5). In contrast,upon determining that network element 102 does not have the most recentversion of the LSPs, reinitialize unit 308 transmits Partial SequenceNumber Packets (PSNPs) for those sequence numbers that are different, atprocess block 610. In an embodiment, PSNPs include those sequencenumbers for the routing information for one particular network element.Reinitialize unit 308 also requests PSNPs for routing data that is notincluded in network element 102. For example, a new network elementcould have been installed while the IS-IS communications of networkelement 102 were non-operational. Accordingly, network element 102 wouldnot be aware or have any routing data associated with this new networkelement.

[0042] Additionally, reinitialize unit 308 receives LSPs from thedesignated network element for those PSNP packets that were transmitted,at process block 612. Reinitialize unit 308 updates the routing datastored within network element 102, at process block 614. Upon storingthe updated routing data, reinitialize unit 308 determines whether apreset timer has expired, at process decision block 615, as describedabove in conjunction with process decision block 512 of FIG. 5.

[0043] Upon determining that this preset timer has not expired,reinitialize unit 308 returns to process block 606 and waits to receiveCSNPs and ‘hello’ packets from the designated network element and theother network elements, respectively. In contrast, upon determining thatthe preset timer has expired, reinitialize unit 308 transmits a firstunmodified ‘hello’ packet and resumes normal operation, at process block616.

[0044] Similar to when network element 102 is the designated networkelement (illustrated by FIG. 5), this preset timer within networkelement 102 allows the other network elements and the designated networkelement time to respond with the required routing data prior to resumingoperation. Accordingly, upon resuming normal operation when IS-IS basedmessaging resumes among network element 102 and the other networkelements in the network, the other network elements do not know that theIS-IS communications of network element 102 have been non-operational.The other network elements, therefore, will not destroy and recreate thecommunication link between themselves and network element 102. Moreover,there is no requirement that the other network elements exchange theirrouting data with network element 102 after the reconstruction of thecommunication link. Accordingly, the data packets that can betransmitted across the communication links between network element 102and the other network elements will not have to be rerouted or lostduring the time when the communication link is destroyed andreconstructed and when the routing data is exchanged between the othernetwork elements and network element 102.

Operation of Network Elements in a Point-to-Point Network Configuration

[0045]FIG. 7 is a block diagram illustrating an embodiment of apoint-to-point network configuration that incorporates embodiments ofthe present invention. In particular, FIG. 7 illustrates network 700that includes network element 702, network element 704, network element706, network element 708, network element 710, and network element 712,such that network elements 702-712 are coupled together in apoint-to-point network configuration, according to embodiments of thepresent invention. Specifically, network element 702 is coupled tonetwork elements 704-710, and network element 712 is coupled to networkelements 704 and 706. In an embodiment, network elements 702-712 can berouters, switches, bridges, or other types of network elements thatswitch data across a network. In another embodiment, network 700 is asystem in which network elements 702-712 share routing information usingthe IS-IS standard. In a further embodiment, network elements 702-712are coupled to other network elements that may be part of othernetworks.

[0046] In an embodiment, network 700 transmits data traffic among thedifferent network elements employing the SONET standard or SDH. However,embodiments of the system in which the present invention is implementedare not so limited, as data traffic among the different network elementscan be transferred using other types of transmission standards. Examplesof other types of transmission standards can include, but are notlimited to, T1, T3, DS3, and DS1 signals.

[0047] The architecture and configuration of network 700 is by way ofexample and not by way of limitation, as embodiments of the presentinvention can be incorporated in other types of systems. For example,other such systems could incorporate less or more network elements intothe network and/or network elements attached thereto. Further, adifferent configuration of the network elements could exist. Moreover,embodiments of the system in which the present invention is implementedare not limited to the network architecture as illustrated in FIG. 7.

[0048]FIG. 8 illustrates a flow diagram for restart communication of anetwork element in a point-to-point network configuration using theIS-IS standard after the IS-IS communications of the network elementhave been non-operational, according to embodiments of the presentinvention. In particular, method 800 illustrates a flow diagram of anetwork element whose IS-IS communications were non-operational and isreinitializing and reestablishing communication with other networkelements in the network. Returning to FIG. 7 to help illustrate, theflow diagram of FIG. 8 will be described in terms of restartingcommunications between network element 702 (acting as the reinitializingnetwork element) and network element 708 (acting as a remote networkelement) in network 700.

[0049] Method 800 commences with the reading of the modified ‘hello’packets from memory 306 (as illustrated in FIG. 4 above) by reinitializeunit 308 within network element 702, at process block 802. Additionally,reinitialize unit 308 also transmits the ‘hello’ packets, whoseunmodified versions were previously transmitted to the remote networkelement, at process block 604 (as described above in conjunction withFIG. 5).

[0050] Similar to embodiments of the broadcast network configuration,this transmission of the stored ‘hello’ packets, which have an increasedtime period, to other network elements with which there is acommunication link allows the reinitializing network element more timeto reinitialize. In particular, if the reinitializing network element isable to transmit a modified ‘hello’ packet to the receiving networkelement before the default time period (which was transmitted with theunmodified ‘hello’ packets) expires, the reinitializing network elementis able to preclude the remote network element from tearing down thecommunication link between itself and the reinitializing networkelement. Accordingly as will be described in more detail below, thisdelay in time allows the restarting network element to reinitialize andupdates its routing information without tearing down and reconstructingthe communication link as well as exchange routing data between the twonetwork elements in order to restart communications between therestarting network elements and those network elements that it isconnected.

[0051] Additionally, reinitialize unit 308 of network element 702transmits CSNP packets to the remote network element, at process block806. In an embodiment of a point-to-point network configuration, eachnetwork element must include routing data for all of the networkelements in the network. Upon receipt of a first hello packet from theremote network element, reinitialize unit 308 of network element 702resumes normal ‘hello’ packet transmissions to the remote networkelement, at process block 808.

[0052] Reinitialize unit 308 of network element 702 also can receive LSPfrom the remote network element if its routing data is out-of-date, atprocess block 810. Additionally, reinitialize unit 308 of networkelement 702 updates the routing information stored within networkelement 702 based on the routing data received from the LSPs, at processblock 812. Upon updating the routing data, reinitialize unit 308determines whether a preset timer has expired, at process decision block814, as described above in conjunction with process decision block 512of FIG. 5. Upon determining that this preset timer has not expired,reinitialize unit 308 returns to process block 806 and transmits CSNPsto the remote network element. In contrast, upon determining that thepreset timer has expired, reinitialize unit 308 resumes normaloperation, at process block 816.

[0053] Similar to the reinitializing network element within a broadcastnetwork configuration, this preset timer within network element 702allows the remote network element to respond with ‘hello’ packets.Accordingly, upon resuming operation when IS-IS based messaging resumesbetween network element 702 and network element 708 (the remote networkelement), network element 708 does not know that the IS-IScommunications of network element 702 have been non-operational. Thisremote network element, therefore, will not destroy and recreate thecommunication link between itself and network element 702. Moreover,there is no requirement that the remote network elements exchange theirrouting data with network element 702 after reconstruction of thecommunication link. Accordingly, the data packets that can betransmitted across the communication links between network element 702and the remote network element will not have to be re-routed or lostduring the time when the communication link is destroyed andreconstructed and when the routing data is exchanged between the remotenetwork element and network element 702.

[0054]FIG. 9 illustrates a flow diagram for updating routing informationwithin a network element, according to embodiments of the presentinvention. In particular, method 900 illustrates the updating of routinginformation within a network element as part of the reinitializationafter the IS-IS communications have become non-operational.Additionally, method 900 of FIG. 9 can be employed in a network elementwithin both a broadcast and point-to-point network configuration, asillustrated in FIGS. 1 and 7 above.

[0055] Method 900 commences with determining adjacencies within thenetwork as well as the gathering of routing data, by reinitialize unit308, at process block 902. As described above, other network elementsincluding the designated network element (in a broadcast configuration),the remote network element (in a point-to-point configuration) as wellas other network elements in the network communicate routing data tonetwork element 102. Accordingly, reinitialize unit 308 determines thenetwork configuration based on this routing data. Additionally,reinitialize unit 308 determines whether the preset timer has expired,at process decision block 904, as described above in conjunction withprocess decision block 512 of FIG. 5.

[0056] Upon determining that the preset timer has not expired,reinitialize unit 308 continues determining adjacencies within thenetwork as well as the gathering of routing data, at process block 902.In contrast, upon determining that the preset timer has expired,reinitialize unit 308 transmits this updated routing data to routinginformation base unit 312. In turn, routing information base unit 312downloads this routing data to the relevant units on the line cards ofthe network element, at process block 906. In an embodiment,reinitialize unit 308 determines routing information using the ShortPath First algorithm. As shown by method 900, network element 102 waitsto update its routing data information until the preset timer hasexpired, thereby having received all of the routing data from therelevant network elements in the network.

[0057] The line cards and control cards included in the differentnetwork elements include memories, processors, and/or ApplicationSpecific Integrated Circuits (“ASICs”). Such memory includes amachine-readable medium on which is stored a set of instructions (i.e.,software) embodying any one, or all, of the methodologies describedherein. Software can reside, completely or at least partially, withinthis memory and/or within the processor and/or ASICs. For the purposesof this specification, the term “machine-readable medium” shall be takento include any mechanism that provides (i.e., stores and/or transmits)information in a form readable by a machine (e.g., a computer). Forexample, a machine-readable medium includes read only memory (“ROM”),random access memory (“RAM”), magnetic disk storage media; opticalstorage media, flash memory devices, electrical, optical, acoustical, orother form of propagated signals (e.g., carrier waves, infrared signals,digital signals, etc.), etc.

[0058] Thus, a method and apparatus for the restart communicationbetween network elements have been described. Although the presentinvention has been described with reference to specific exemplaryembodiments, it will be evident that various modifications and changesmay be made to these embodiments without departing from the broaderspirit and scope of the invention. For example, different networkconfigurations using the IS-IS standard for sharing routing informationare possible. Accordingly, the specification and drawings are to beregarded in an illustrative rather than a restrictive sense.

What is claimed is:
 1. A method for restarting communication between afirst network element and a second network element in a network, themethod comprising: transmitting a modified hello packet to the secondnetwork element, the modified hello packet including a time value thatis greater than a time value of a hello packet that was transmitted tothe second network element prior toInternational-System-International-System (IS-IS) network communicationsin the first network element becoming non-operational; and updatingrouting information within the first network element throughtransmission of Complete Sequence Number Packets of the IS-IS standardto the second network element, independent of tearing down acommunication link between the first network element and the secondnetwork element after IS-IS network communications in the first networkelement have become non-operational.
 2. The method of claim 1, whereinthe network includes a broadcast network configuration.
 3. The method ofclaim 1, wherein the network includes a point-to-point networkconfiguration.
 4. The method of claim 1, wherein the modified hellopacket is stored in a local memory of the first network element.
 5. Amethod comprising: reinitializing a transmitting network element afterInternational-System-International-System (IS-IS) network communicationsin the transmitting network element has been non-operational, whereinthe transmitting network element is a designated network element in abroadcast network configuration, the reinitializing comprising:transmitting a request for routing data under the IS-IS standard to anumber of receiving network elements; receiving routing data from thenumber of receiving network elements; updating routing data within thetransmitting network element based on the received routing data; andresuming operation upon determining that a timer for initialization hasexpired, independent of tearing down a communication link between thetransmitting network element and the number of receiving networkelements.
 6. The method of claim 5, further comprising: transmittingmodified hello packets to the number of receiving network elements, themodified hello packets including a time value that is greater than atime value of a hello packet that was transmitted to the number ofreceiving network elements prior toInternational-System-International-System (IS-IS) network communicationsin the transmitting network element becoming non-operational.
 7. Amethod comprising: reinitializing a transmitting network element afterInternational-System-International-System (IS-IS) network communicationsin the transmitting network element has been non-operational, whereinthe transmitting network element is a network with a point-to-pointnetwork configuration, the reinitializing comprising: transmitting, fromthe transmitting network element, Complete Sequence Number Packets(CSNPs) based on the IS-IS standard to a receiving network element inthe network; receiving Link State Packets (LSPs) from the receivingnetwork element based on the CSNPs transmitted; and updating routingdata stored within the transmitting network element based on thereceived LSPs; resuming IS-IS network communications in the transmittingnetwork element upon receipt of a first hello packet from the receivingnetwork element since starting reinitialization of the transmittingnetwork element, independent of tearing down a communication linkbetween the transmitting network element and the receiving networkelement; and resuming operation of transmitting network element uponexpiration of a preset timer for initialization.
 8. The method of claim7, further comprising: transmitting modified hello packets to thereceiving network element, the modified hello packets including a timevalue that is greater than a time value of a hello packet that wastransmitted to the receiving network element prior to IS-IS networkcommunications in the transmitting network element becomingnon-operational.
 9. A network element comprising: a memory; a heartbeatunit coupled to the memory, the hello unit to transmit a modified hellopacket to a different network element in a network, wherein the modifiedhello packet is to be stored in the memory and is to include a timevalue that is greater than a time value of a hello packet that is to betransmitted to the different network element prior toInternational-System-International-System (IS-IS) network communicationsin the network element becoming non-operational; and a reinitialize unitcoupled to the heartbeat unit, the reinitialize unit to update routinginformation within the network element through transmission of CompleteSequence Number Packets of the IS-IS standard to the different networkelement, independent of tearing down a communication link between thenetwork element and the different network element after IS-IS networkcommunications in the network element have become non-operational. 10.The network element of claim 9, wherein the network includes a broadcastnetwork configuration.
 11. The network element of claim 9, wherein thenetwork includes a point-to-point network configuration.
 12. Amachine-readable medium that provides instructions for restartingcommunication between a first network element and a second networkelement in a network, which when executed by a machine, causes themachine to perform operations comprising: transmitting a modified hellopacket to the second network element, the modified hello packetincluding a time value that is greater than a time value of a hellopacket that was transmitted to the second network element prior toInternational-System-International-System (IS-IS) network communicationsin the first network element becoming non-operational; and updatingrouting information within the first network element throughtransmission of Complete Sequence Number Packets of the IS-IS standardto the second network element, independent of tearing down acommunication link between the first network element and the secondnetwork element after IS-IS network communications in the first networkelement have become non-operational.
 13. The machine-readable medium ofclaim 12, wherein the network includes a broadcast networkconfiguration.
 14. The machine-readable medium of claim 12, wherein thenetwork includes a point-to-point network configuration.
 15. Themachine-readable medium of claim 12, wherein the modified hello packetis stored in a local memory of the first network element.
 16. Amachine-readable medium that provides instructions, which when executedby a machine, causes the machine to perform operations comprising:reinitializing a transmitting network element afterInternational-System-International-System (IS-IS) network communicationsin the transmitting network element has been non-operational, whereinthe transmitting network element is a designated network element in abroadcast network configuration, the reinitializing comprising:transmitting a request for routing data under the IS-IS standard to anumber of receiving network elements; receiving routing data from thenumber of receiving network elements; updating routing data within thetransmitting network element based on the received routing data; andresuming operation upon determining that a timer for initialization hasexpired, independent of tearing down a communication link between thetransmitting network element and the number of receiving networkelements.
 17. The machine-readable medium of claim 16, furthercomprising: transmitting modified hello packets to the number ofreceiving network elements, the modified hello packets including a timevalue that is greater than a time value of a hello packet that wastransmitted to the number of receiving network elements prior toInternational-System-International-System (IS-IS) network communicationsin the transmitting network element becoming non-operational.
 18. Amachine-readable medium that provides instructions, which when executedby a machine, causes the machine to perform operations comprising:reinitializing a transmitting network element afterInternational-System-International-System (IS-IS) network communicationsin the transmitting network element has been non-operational, whereinthe transmitting network element is a network with a point-to-pointnetwork configuration, the reinitializing comprising: transmitting, fromthe transmitting network element, Complete Sequence Number Packets(CSNPs) based on the IS-IS standard to a receiving network element inthe network; receiving Link State Packets (LSPs) from the receivingnetwork element based on the CSNPs transmitted; and updating routingdata stored within the transmitting network element based on thereceived LSPs; resuming IS-IS network communications in the transmittingnetwork element upon receipt of a first hello packet from the receivingnetwork element since starting reinitialization of the transmittingnetwork element, independent of tearing down a communication linkbetween the transmitting network element and the receiving networkelement; and resuming operation of transmitting network element uponexpiration of a preset timer for initialization.
 19. Themachine-readable medium of claim 18, further comprising: transmittingmodified hello packets to the receiving network element, the modifiedhello packets including a time value that is greater than a time valueof a hello packet that was transmitted to the receiving network elementprior to IS-IS network communications in the transmitting networkelement becoming non-operational.